Underwater energy storage system and power station powered therewith

ABSTRACT

An underwater energy storage system includes a tank for storing a compressed gas that is adapted to be stored underwater. The tank includes at least one water opening through which water from surrounding environment can flow into and out of the tank, and at least one gas opening through which the compressed gas is received. The underwater energy storage system further includes at least one duct communicating between the at least one opening for gas flow and a source of compressed gas and a compartment constructed over a roof of the tank, wherein said compartment is adapted for receiving weights at a sinking site of the tank.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/585,236 filed on May 3, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/084,558 filed on Mar. 30, 2016, which is acontinuation of U.S. patent application Ser. No. 14/446,400 filed onJul. 30, 2014, now U.S. Pat. No. 9,309,046, which is a continuation ofU.S. patent application Ser. No. 13/577,254 filed on Aug. 5, 2012, nowU.S. Pat. No. 8,801,332, which is a National Phase of PCT PatentApplication No. PCT/IL2011/000157 having International Filing Date ofFeb. 15, 2011, which claims the benefit of priority under 35 USC §119(e) of U.S. Provisional Patent Application No. 61/304,499 filed onFeb. 15, 2010. The contents of the above applications are allincorporated by reference as if fully set forth herein in theirentirety.

FIELD OF THE INVENTION

The present invention, in some embodiments thereof, relates tounderwater energy storage and, more particularly, but not exclusively,to underwater energy storage of compressed air.

BACKGROUND OF THE INVENTION

Although renewable energy from natural resources such as sunlight, wind,rain, and tides are typically clean, plentiful and relatively cheap, itsuse has been limited due to an inherent problem that renewable energy isnot always available on demand. Compressed air energy storage is a wayto store energy generated during periods of low energy demand for useduring periods of high energy demands. It has been proposed to storecompressed air in a high pressure environment such as deep underwater toavoid the costs of high-pressure vessels for storing the compressed air.

A compressed air energy storage device in development stages isdescribed in an article published on Apr. 28, 2010 onwww(dot)energystorageforum(dot)com/tag/compressed-air/ downloaded fromthe internet on Jan. 27, 2010. The article discloses a pumpkin-shaped,underwater, compressed-air-storage devices being trialed at theUniversity of Nottingham. It is described that thecompressed-air-storage devices, constructed from steel and polymer, aredesigned to be pumped full of high-pressure air during times of highwinds and low demand, with the stored energy used to turn turbines tocreate electricity when needed on the grid. The article states that thecompressed-air-storage devices being trialed at the University ofNottingham could prove key to overcoming one of the main obstacles toEurope's long-term ambitions for utility-scale renewable-energyproduction—that peak power-generating times from offshore wind farmsrarely match peak demands for electricity onshore.

Japanese Patent Application No. JP54011517 published on Jan. 27, 1979,entitled “Marine pressurized water type energy storing method,” thecontents of which is incorporated by reference, describes a rigid domeshaped air storage tank including a water valve and an air pipe forstoring pressure energy in a pressurized water vessel placed in or onthe bottom of the sea with compressed air pumped in from an aircompressor set in the marine space.

Japanese Patent Application No. JP63239320 published on Oct. 5, 1988,entitled “Underwater Energy Storage Device,” the contents of which isincorporated by reference, describes a hollow rigid bottomless caseplaced on the bottom of the sea for storing pressurized air. During thenighttime or the like where the surplus power is produced, a compressoris operated to feed pressurized air into the hollow case through aconnecting pipe, and then, by forcing the seawater through a waterpassage hole, the electrical energy is stored as an air-pressure energyin the case. During the daytime, a generator is operated by making useof the pressurized air stored in the case.

Japanese Patent Application No. JP2271032, published on Nov. 6, 1990,entitled “Compressed air storage device for underwater installation andsubmerging method thereof,” the contents of which is incorporated byreference, describes an underwater installation compressed air storagedevice including main compressed air storage tank of bottomless shellconstruction and an additional weight adding part in its lower part. Itis described that the device is softly landed to the sea bottom byreleasing compressed air from a work deck barge and special underwaterconcrete is placed in the additional weight adding part through a pipe.The storage device is connected to a compressor and a turbine on theground with a pipe.

Japanese Patent Application No. JP4121424 published on Apr. 22, 1992,entitled “Air storage power generation method and air storage powergeneration plant,” the contents of which is incorporated by reference,describes an underwater compressed air storage tank that floats abovethe seabed and has an opening at the bottom through which water isintroduced and expelled. Water surrounding the tanks cools the air sothat the temperature is decreased, while the pressure is maintainedconstant. Under condition of power shortage, the cooled compressed airis feed to a boost compressor and afterwards supplied to a combustor ascombustion air through an air pipeline.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a utility-scaled underwater energy storage system andmethod for storing compressed air underwater. According to someembodiments of the present invention, the underwater energy storagesystem includes features for withstanding and/or counterbalancing forcesapplied on a compressed air storage tank due to differential pressureconditions that exist over a height of the storage system when storedunderwater. According to some embodiments of the present invention, theunderwater energy storage system includes features for submerging andanchoring the storage system underwater. According to some embodimentsof the present invention, the underwater energy storage system includesfeature for cooling compressed air as it flows from a compressor to astorage tank of the underwater energy storage system. According to someembodiments of the present invention, the underwater energy storagesystem is an adiabatic storage system including features for storingheat produced during compression of the air and using the stored heat toheat air discharged from the underwater energy storage system.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: a tank forstoring a compressed gas that is adapted to be stored underwater, thetank comprising: at least one water opening through which water fromsurrounding environment can flow into and out of the tank; and at leastone gas opening through which the compressed gas is received; at leastone duct communicating between the at least one opening for gas flow anda source of compressed gas; and a compartment constructed over a roof ofthe tank, wherein said compartment is adapted for receiving weights at asinking site of the tank.

Optionally, the compartment is formed with a banister encompassing theroof of the tank.

Optionally, the banister is an integral part of walls of the tank thatextends above a height of the roof.

Optionally, the compartment is partitioned with partitioning wallsadapted to provide structural support for the roof of the tank.

Optionally, the tank includes sloped walls, and wherein the banister atleast partially encompasses the walls of the tank.

Optionally, the compartment includes a door, wherein the door providesfor releasing weights received in the compartment when opened.

Optionally, the weights include at least one of rocks, sand and gravel.

Optionally, the tank includes walls that have a thickness that increasesover a height of the walls.

Optionally, the tank includes walls with structural reinforcements,wherein an amount of the reinforcement provided increases over a heightof the tank.

Optionally, the tank is partitioned into a plurality of chambers, saidchambers include chamber walls with gas openings that provide free gasflow between the chambers and wherein each of the chambers includeswater opening through which water from surrounding environment can flow.

Optionally, a chamber wall that surrounds a chamber that directlycommunicates with the at least on duct through which the compressed gasis received, is provided with added reinforcements.

Optionally, the at least one duct through which the compressed gas isreceived branches into a plurality of ducts each of which directlycommunicates with one of the chambers of the tank.

Optionally, the system comprises: a plurality of tanks; and gas ductsconnected between gas openings of each of the plurality of tanks,wherein the gas ducts provide free gas flow between the plurality oftanks.

Optionally, the system comprises a water duct connected the at least onewater opening and extending upward therefrom, said duct adapted toprovide a water opening at a height above the water opening of the tank.

Optionally, the system comprises an extension extending from a floor ofthe tank, the extension defining an open channel in which weights can becontained for anchoring the tank on a bed of a water body.

Optionally, the tanks includes prongs extending outward from a floor ofthe tank, wherein said prongs are adapted to be embedded in a bed of awater body for stabilizing the tank on the bed of the water body.

Optionally, the tank is casted with concrete.

Optionally, the tank includes inner walls that are coated with a metallayer.

Optionally, a thickness of the metal layer increases over a height ofthe tank.

Optionally, the tank includes outer walls that are coated with a metallayer.

Optionally, the at least one duct communicating between the at least oneopening for gas flow and a source of compressed gas is lined with aplurality of ribs adapted to cool the compressed gas as it flows fromthe source to the tank.

Optionally, at least a portion of the ribs are outer ribs that encompassan outer diameter of the duct and wherein the outer ribs are structuredto be in line with a direction of current flow in the sinking site ofthe system.

Optionally, the system comprises at least one duct communicating betweenthe at least one opening for gas flow in the tank and a pneumaticdevice.

Optionally, the system comprises a heat exchange unit for transferringheat generated by the source of compressed gas to gas flowing from theat least one duct communicating between the at least one opening for gasflow in the tank and a pneumatic device.

Optionally, the heat exchange unit includes a heat exchange pool formedbetween a damn constructed at a distance from a beach and the beach.

Optionally, the heat exchange unit includes at least one thermal energystorage element through which the at least one duct communicatingbetween the at least one opening for gas flow and a source of compressedgas and the at least one duct communicating between the at least oneopening for gas flow in the tank and a pneumatic device pass through.

Optionally, the system comprises a heat exchange unit adapted to harnesscooling of gas discharged from the tank for desalinating water.

Optionally, the compressed gas is compress air.

Optionally, the compressed gas is condensed carbonic gas.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: a pluralityof tanks for storing compressed air underwater, wherein each of thetanks include at least one water opening through which water from asurrounding water body can flow into and out of the tank and at leastone air opening for receiving and discharging the compressed air; afirst duct for communicating air flow between the at least one airopening of at least one of the plurality of tanks and a source ofcompressed air; and at least one second duct for communicating air flowbetween the at least one air opening of each tank.

Optionally, the system comprises a water duct connected to the at leastone water opening of each of the plurality of tanks and extending upwardtherefrom, said duct adapted to provide a water opening at a heightabove the water opening of the tank.

Optionally, at least a portion of the plurality of tanks are partitionedinto a plurality of chambers, said chambers include chamber walls withair openings that provide free air flow between the chambers and whereineach of the chambers includes water opening through which water fromsurrounding environment can flow.

Optionally, at least a portion of the plurality of tanks includes wallswith structural reinforcements, wherein an amount of the reinforcementprovided increases over a height of the tank.

Optionally, t least one an inner or outer wall of the plurality of tanksis coated with a metal layer.

Optionally, the at least one duct communicating between the at least oneopening for air flow and a source of compressed air is lined with aplurality of ribs adapted to cool the compressed air as it flows fromthe source to the tank.

Optionally, the system comprises at least one duct communicating betweenthe at least one opening for air flow in at least one of the pluralityof tanks and a pneumatic device.

Optionally, the system comprises a heat exchange unit for transferringheat generated by the source of compressed gas to air flowing from theat least one duct communicating between the at least one opening for gasflow in at least one of the plurality of tanks and a pneumatic device.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: a bellshaped tank with a concave shaped wall for storing compressed airunderwater, wherein the tank includes a water opening through whichwater from a surrounding water body can flow into and out of the tankand at least one air flow opening for receiving compressed air; and atleast one duct extending from the at least one air flow opening and asource of compressed air.

Optionally, a shape of the tank is defined to counterbalance an increasein tensile forces along a height of the tank due to an increase inpressure drop along a height of the wall.

Optionally, a change in a diameter of the tank over the height isdefined to reduce tensile forces on wall of tank as the pressure dropacross the wall increases.

Optionally, the tank is shaped such that a diameter of the tank at agiven height multiplied by the given height is constant for all heightsof the tank.

Optionally, the system comprises a water duct connected to the wateropening and extending upward therefrom, said duct adapted to provide awater opening at a height above the water opening of the tank.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: a tank forstoring compressed gas underwater, wherein the tank includes at leasttwo stories, wherein the stories are fluidly connected through at leastone opening between a ceiling of a lower story and a floor of an upperstory, the opening adapted to provide free flow of compressed gas andwater, wherein the lower story of the tank includes at least one wateropening through which water from a surrounding water body can flow intoand out of the tank and wherein the upper story of the tank includes atleast one air flow opening for receiving compressed air, and wherein adiameter or an extent of the upper story of the tank is less than adiameter or an extent of the lower story of the tank; and at least oneduct extending from the at least one air flow opening and a source ofcompressed air.

Optionally, the diameter of the upper story is defined to counterbalancelarger tensile force on walls of the tank in the upper story as comparedto tensile force on the walls of the tank in the lower story.

Optionally, the system comprises a plurality of tanks; and air ductsconnected between air opening of each of the plurality of tanks, whereinthe air ducts provide free gas flow between the plurality of tanks.

Optionally, the at least one duct extending from the at least one airflow opening and a source of compressed air is lined with a plurality ofribs adapted to cool the compressed air as it flows from the source tothe tank.

Optionally, the system comprises at least one duct communicating betweenthe at least one air flow opening in the tank and a pneumatic device.

Optionally, the system comprises a heat exchange unit for transferringheat generated by the source of compressed air to air flowing from theat least one duct communicating between the at least one air flowopening in the tank and the pneumatic device.

According to aspects of some embodiments of the present invention thereis provided n underwater energy storage system comprising: a rigid tankfor storing a compressed gas that is adapted to be stored underwater,the tank includes: at least one opening through which water fromsurrounding environment can flow into and out of the tank; and anopening through which the compressed gas is received; and at least oneduct communicating between the at least one opening for gas flow and asource of compressed gas; and a collapsible bag housed in the rigid tankincluding an opening that communicates with the opening through whichthe compressed gas is received, wherein the collapsible bag is adaptedto receive and contain the compressed gas.

Optionally, the gas is condensed carbonic gas.

Optionally, the system comprises a compartment constructed over a roofof the tank, wherein said compartment is adapted for receiving weightsat a sinking site of the tank.

Optionally, the tank is rests on a bed of a water body.

Optionally, the bag is partially connected to a floor of the tank.

Optionally, an inner wall of the tank is coated with friction protectivematerial.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: anunderwater storage tank for storing compressed air, wherein the tank isformed from a roof construction rigidly connected to walls of anunderwater geological formation, wherein said roof construction includesat least one opening though which compressed air is received; and atleast one duct communicating between the at least one opening for airflow and a source of compressed air.

Optionally, the system comprises at least one duct communicating betweenthe at least one opening for gas flow in the tank and a pneumaticdevice.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: a tank forstoring a compressed air that is adapted to be stored underwater,wherein the tank is a floorless tank, the tank including: a collapsibleportion, wherein the collapsible portion includes an opening adapted tocommunicate with a duct through which the compressed air is received andan open bottom from which water can enter and exit the collapsibleportion; and a rigid portion adapted to provide a rigid construction formaintaining the bottom open; and at least one duct communicating betweenthe opening for air flow and a source of the compressed air.

Optionally, the collapsible portion is protected with a rigid cage.

Optionally, the system comprises an anchoring element attached to therigid portion, wherein the anchoring element is adapted to maintain thetank at a given height above a bed of a water body.

According to aspects of some embodiments of the present invention thereis provided an underwater energy storage system comprising: anunderwater storage tank for storing compressed air, wherein the tank isformed from a rigid cover forming a cavity therein, wherein the tankincludes an opening for air flow through which compressed air isreceived and is bottomless, and wherein the tank is adapted to floatover a bed of the water body; at least one anchoring element holding theunderwater storage tank for anchoring the storage tank at a height abovethe bed of a water body; at least one duct communicating between theopening for air flow and a source of the compressed air.

Optionally, the storage tank is dome shaped.

Optionally, the storage tank has a shape of a truncated sphere.

Optionally, the storage tank is constructed from at least one of metal,concrete and a rigid polymer.

Optionally, the at least one anchoring element is in a form of a netconnected to a weight, where the net is adapted for encompassing thestorage tank.

According to aspects of some embodiments of the present invention thereis provided a method for casting an underwater energy storage system ata sinking site, the method comprising: providing a frame defining wallsof an underwater storage tank, wherein the frame is fitted with duct fordefining an opening for water flow communication between the tank and asurrounding water body, and wherein the frame is fitted with duct fordefining an opening for air flow; blocking at least one of the openingfor water flow communication and the opening for air flow; transportingthe frame to a sinking site; and pouring casting material in the frame.

Optionally, the method comprises releasing blocking of the at least oneof the opening for water flow communication and the opening for air flowso that the tank can sink.

Optionally, the method comprises controlling sinking with a chain ofbuoys.

According to aspects of some embodiments of the present invention thereis provided a thermal energy storage element in the form of a sphereconstructed from concrete or ceramic material and embedded with at leastone metal rod, wherein the metal rod at least partially protrudesthrough the sphere.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a simplified schematic drawing of an exemplary underwaterenergy storage system and a power station powered therewith inaccordance with some embodiments of the present invention;

FIG. 2 is a simplified schematic diagram showing exemplary forces actingon an underwater storage tank due to differential pressure along aheight of the underwater storage tank in accordance with someembodiments of the present invention;

FIGS. 3A and 3B are simplified schematic drawing of exemplary underwaterenergy storage systems with reinforced construction for withstandingpressure drops across walls of the storage tank in accordance with someembodiments of the present invention;

FIGS. 4A, 4B and 4C are simplified schematic drawings of exemplaryunderwater energy storage systems including a storage tank whosediameter decreases as a function of tank height in accordance with someembodiments of the present invention;

FIGS. 5A and 5B are simplified schematic drawings of exemplaryunderwater energy storage systems including a cylindrical storage tankthat is partitioned in accordance with some embodiments of the presentinvention;

FIG. 6 is a simplified schematic drawing of exemplary underwater energystorage system including a cuboid shaped storage tank that ispartitioned in accordance with some embodiments of the presentinvention;

FIGS. 7A and 7B are simplified schematic drawings of exemplaryunderwater energy storage systems including partitioned tank withreinforced walls around an air entrance chamber in accordance with someembodiments of the present invention;

FIG. 8 is a simplified schematic drawing of an exemplary underwaterenergy storage system including a plurality of inlet/outlet ducts thatconverge into a single duct in accordance with some embodiments of thepresent invention;

FIG. 9 is a simplified schematic drawing of an exemplary underwaterenergy storage system including a plurality of storage tank modules thatare fluidly connected in accordance with some embodiments of the presentinvention;

FIGS. 10A and 10B are simplified schematic drawings of exemplaryunderwater energy storage systems including a floorless storage tankthat is anchored at a height above a seabed in accordance with someembodiments of the present invention;

FIG. 11 is a simplified schematic drawing of an exemplary underwaterenergy storage system partially formed from natural underwater landscapeformations in accordance with some embodiments of the present invention;

FIGS. 12A, 12B and 12C are simplified schematic drawings of exemplaryunderwater energy storage systems including a flexible storage bag inaccordance with some embodiments of the present invention;

FIG. 13 is a simplified schematic drawing of an exemplary underwaterenergy storage system including a flexible compressed energy storagecontainer housed in rigid storage underwater tank in accordance withsome embodiments of the present invention;

FIGS. 14A and 14B are simplified schematic drawings showing an exemplarymethod for casting and sinking an exemplary underwater energy storagesystem in accordance with some embodiments of the present invention;

FIG. 15 is a simplified schematic drawing of an exemplary underwaterenergy storage system including an inlet pipe for cooling compressed airin accordance with some embodiments of the present invention;

FIG. 16 is a simplified schematic drawing of an exemplary heat exchangeand heat preservation system for use with an underwater energy storagesystem in accordance with some embodiments of the present invention;

FIG. 17 is a simplified schematic drawing of a variety of exemplary heatpreservation pools for use with an underwater energy storage system inaccordance with some embodiments of the present invention;

FIG. 18 is a simplified schematic drawing of an exemplary heat exchangeunit for desalinating water for use with an underwater energy storagesystem in accordance with some embodiments of the present invention; and

FIGS. 19A and 19B are simplified schematic drawings of exemplary thermalenergy storage elements for use with an underwater energy storage systemin accordance with some embodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates tounderwater energy storage and, more particularly, but not exclusively,to underwater energy storage of compressed air.

According to some embodiments of the present invention there is providedan underwater energy storage unit including a rigid storage tankequipped with a structure for receiving and containing weights over arooftop of the storage tank that can act to counterbalance pressuredifferences between compressed air within the tank and pressure level ofwater at a height of the roof of the tank. Optionally, the structure isa banister and the weights include rocks and sand that are poured overthe rooftop. In some exemplary embodiments, the structure for receivingweights includes a door for expelling the weights on demand, e.g. tofloat the tank above water.

The present inventors have found that significant pressure drops mayexist across an upper portion of the walls where the outside waterpressure is significantly lower than an inner pressure of the tank.Optionally, the tank is designed to be wide and short to avoid largepressure differences at a height above the floor of the tank. Accordingto some embodiments of the present invention, the tank is constructedfrom walls that are reinforced in a gradual manner to counterbalance thegradually changing pressure drop along a height of the tank. Accordingto some embodiments of the present invention, the tank is shaped with adiameter that decreases over a height of the tank. Optionally, adiameter of the tank along a height of the structure is defined tocounterbalances increasing tensile forces along a height of the wall dueto increase in pressure drop across the walls. Optionally, the diameterof the tank steadily decreases so that the tensile forces on the wallsdue to pressure drop are maintained constant over the height of thetank.

According to some embodiments of the tank includes one or more openingsthrough which water freely flows in and out of the tank. Optionally, apipe connected to one or more openings provides a water flow opening ata height above a seabed so that water that flows into the tank does notinclude solid particles typically found near the seabed. Optionally thepipe provides for maintaining free water flow, even when the tank sinksinto the seabed. Typically, the tank also includes one or more openingsconnected to pipes through which compressed air can flow into and out ofthe tank. Optionally and air flow pipe that directs air from acompressor to the tank includes formed with heat exchange ribs forreducing the temperature of the air before entering the underwater tank.

According to some embodiments of the present invention, the underwatertank is partitioned into a plurality of chambers that have air andoptionally water flow communication between them. Optionally thepartitioning provides additional reinforcements to the tank structure.Optionally, a cavity defined by the banister above the roof of the tankis also partitioned to provide reinforcement to walls and ceiling of thetank. Optionally, the chambers also have water flow communicationbetween them. According to some embodiments of the present invention, anair flow pipe directly communicates with one or more of the compartmentsof a storage tank. Optionally, a single air flow pipe branches into aplurality of pipes that directly communicate with each chamber and/orcell in a single tank.

According to some embodiments of the present invention the underwaterenergy storage system is constructed from a plurality of tanks, e.g.modular units that have air flow communication between them. Optionally,a single air flow pipe branches into a plurality of pipes that directlycommunicate with each of the modular units. The present inventors havefound that by constructing underwater energy storage system from aplurality of modular units, each of the units can have a relativelysmaller volume and typically a more structurally sound construction dueits size. Additionally, such a system can be more cost effective sinceit can be composed from standardized sized units.

According to some embodiments of the present invention, the underwaterstorage tank is partially constructed from a flexible material.Optionally, the tank is floorless and is anchored at a height above theseabed. Optionally, the tank is partially constructed from existinggeological formations, e.g. a canyon. Optionally, a rigid underwaterstorage tank houses a flexible bag for storing a gas and/or fluid.Optionally the rigid underwater storage tank includes water flow openingthat provides free water flow in and out of that tank to counterbalancechanges in a volume of the housed flexible bag.

According to some embodiments of the present invention, the underwaterstorage tank is constructed from a frame or mold that defines an innercavity that is cast with cement. According to some embodiments of thepresent invention, the frame is transported to a sinking site and theunderwater storage tank is cement casted on site. Optionally, a frame ormold defines a plurality of underwater tanks that can be in fluidcommunication. Optionally, one or more water flow pipes and air flowpipes are fitted onto frame prior to concrete (or cement) casting.

According to some embodiments of the present invention, the underwaterenergy storage system is an adiabatic system that stores heat generatedduring air compression and used the stored heat to expand and heatdischarged air and/or is used to desalinate water. Optionally, energy isstored in heat exchange reservoirs and/or in thermal energy storageelements.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description and/or illustrated inthe drawings. The invention is capable of other embodiments or of beingpracticed or carried out in various ways.

Referring now to the drawings, FIG. 1 illustrates a simplified schematicdrawing of an exemplary underwater energy storage system and powerstation powered therewith in accordance with some embodiments of thepresent invention. According to some embodiments of the presentinvention, an underwater energy storage system 100 stored in a waterbody 50, e.g. a sea, lake or reservoir level and anchored on a bed 80 ofthe water body 50 includes a rigid tank 10, an inlet air duct 31 forreceiving compressed air, an outlet air duct 33 for releasing compressedair, and one or more water ducts 22 and/or water openings 20 forreceiving and expelling water to and from the underwater environment.Typically, tank 10 includes a floor 65 so that flow in and out of tank10 is only provided through dedicated openings, e.g. openings 20, 21 forwater flow and 31, 32 for air flow. Typically, tank 10 is filled withwater 25 and compressed air 35.

According to some embodiments of the present invention, air compressedwith a compressor 94 is pumped and/or feed through inlet pipe 31 intotank 10 for storage and released through outlet pipe 32 when an energysource is required. Typically, air is compressed during off-peaks hours,stored in tank 10 and then controllably released during peak hours whenadditional energy is required. Optionally, energy from waves areharnessed to compress air. In some exemplary embodiments, air releasedfrom tank 10 is used to drive a turbine 92, e.g. a wind turbineconnected with electricity main 97. Optionally, wind turbine 92 directlyextends from tank 10, e.g. tank 10 serves as a structural base for windturbine 92. Typically, inlet duct (or pipe) 31 and outlet duct (or pipe)32 are equipped with valves 39 for controlling flow through the pipes.Typically, ducts 31 and 32 are connected to openings in an upper portionof tank 10 where air is present. Optionally, ducts 2, 3 are connected toone or more openings in roof 48 of tank 10. In some exemplaryembodiments, inlet and outlet flow of air is provided with a single ductconnected to a single opening in tank 10. Optionally, a singleinlet/outlet duct connected to storage tank 10 branches into one or moreadditional ducts, e.g. inlet and/or outlet ducts. Ducts 31 and 32 may beeither rigid or flexible.

According to some embodiments of the present invention, water is free toflow into and out of water ducts 22 and/or water openings 20 to balancepressure level in tank 10 as air flows into and out of tank 10.Typically, compressed air 35 is stored in tank 10 at constant pressure.In some exemplary embodiments, duct or pipe 22 is connected to a lowerpart of tank 10 typically below the expected minimum water level andextends upwards, e.g. with a slope so that water can be collected intotank 10 from a height above bed 80 of the water body 50 where the water,e.g. sea or lake water is expected to be clean from particles such assand and dust. Optionally, duct or pipe 22 is several meters long, e.g.5-50 meters or 30 meters to provide unobstructed water flow even incases when the tank sinks into bed 80 of the water body. Optionally,tank 10 includes a plurality of openings for water flow optionallyconnected to water flow ducts to provide sufficient water flow in andout of the tank even in cases when one or more of the openings areobstructed. Optionally openings 20 and/or ducts 22 are equipped withfilters to prevent obstruction of water flow openings.

In some exemplary embodiments, an electricity producing turbine (notshown) is installed in one or more water openings 20 or openings ofducts 22 and is used to generate electricity during periods of airdischarge when water flow is rushed into tank 10. In some exemplaryembodiments, oil 66 is provided in tank 10 to cover water surface 77 andthereby prevent evaporation of water in tank 10. Optionally, floatingstructures, e.g. Styrofoam™ is added to cover water surface 77 andthereby prevent evaporation of water in tank 10. Alternatively, water 77is not covered with a material to prevent evaporation.

Typically, air pressure in tank 10 is maintained at a pressure leveldefined by a depth of water 25 in tank 10 and depth under water level 78in which tank 10 is submerged. Since the air pressure in the structureis typically close to or the same as the external water pressure,storing tank 10 in deeper water, increases the pressure of air 35 andthereby the amount of air and energy that it can store.

According to some embodiments of the present invention, underwaterenergy storage system 100 includes a compartment 40 over ceiling 47 oftank 10 for storing weights and/or fillers 49. In some exemplaryembodiments, weights 49 are composed from sand, rocks gravel and/orrecycled wastes that are poured into and/or positioned in compartment 40during and/or after submersion of tank 10 underwater. Optionally weights49 is cement poured into compartment 40. In some exemplary embodiments,compartment 40 is defined by a banister 45 that surrounds roof 48 and/ortank 10. Optionally, underwater energy storage system 100 includes aframe 244 that extends from tank 10, e.g. from floor 17 and forms acavity 43 for receiving weights 49. According to some embodiments of thepresent invention, floor 17, frame and/or banister 244 are integralparts of tank 10, e.g. a single unit with tank 10. According to someembodiments of the present invention, weights 49 provide a gravitationforce 84 on tank 10 for resisting floatation of the tank. In someexemplary embodiments, compartment 40 is sized and designed to contain avolume and mass of weights 49 that can provide a gravitational forcethat counterbalances pressure drop across roof 48 generating an upwardforce 82. This feature is explained in more detail herein below.

Optionally, floor 65 includes prongs and/or extensions 18 that aredesigned to be buried in seabed 80 and thereby stabilize tank 10 on theseabed. Optionally prongs 18 are an integral part of tank 10 and areconstructed from cement. Alternatively, prongs 18 are constructed frommetal extending out from flow 65.

According to some embodiments of the present invention, tank 10 isconstructed from one or more of concrete, cement, metal and plastic.Typically, tank 10 is constructed as a single unit for durability.Optionally, tank 10 is constructed from cement with fibers mixed intothe cement that may increase durability of tank 10 and prevent cracking.Optionally fibers from one or more of polymer material, glass and metalis mixed into the cement. The present inventor has found that the typesof forces and directions of forces applied on the tank can vary greatlydue to changing conditions in and around the tank. Changes in conditionsmay be due for example to changes in the volume of water and/or air inthe tank, to changes in temperature drop across the walls of the tankand/or due to changes in water currents. According to some embodimentsof the present invention, tank 10 is constructed from a composite ofdifferent types of materials to provide durability against varyingforces, e.g. tensile and compressive forces that may be applied on tank10 over time. In some exemplary embodiments, tank 10 is constructed fromreinforced concrete, e.g. concrete reinforced with metal to providedurability against both tensile and compressive forces, e.g. metal forproviding durability against tensile forces and concrete for providingdurability against compressive forces. In some exemplary embodiments,tank 10 is coated inside and/or outside with metal, alloys, polymers oroils. Optionally, metal coating is used to prevent leakage of airthrough cement and to facilitate damage repairs by patching or welding.Optionally, tank 10 is constructed with reinforced concrete thatincludes a metal and/or polymer layer on at least one of the inside andoutside walls. Optionally corrosion and/or cathodic inhibitors are usedto retard corrosion. Optionally, tank 10 may be cylindrical in shape andhave a diameter between 20-200 meters and/or between 30-120 meters witha height of between 5-20 meters and/or 5-12 meters. In some exemplaryembodiments, compartment 40 has banister 45 with a height that isbetween 40-100 percent, e.g. 60 percent of a height of tank 10.

In some exemplary embodiments, tank 10 may be fully or partially builton land, transported by sea to the desired location and sunk. In someexemplary embodiments, concrete is poured above or under sea level in ashell that defines structure of tank 10. According to some embodimentsof the present invention, rocks or the like is piled over tank 10 toprevent its floating when air is being compressed into it.

Reference is now made to FIG. 2 illustrates a simplified schematicdiagram showing exemplary forces acting on an underwater storage tankdue to differential pressure along a height of the underwater storagetank in accordance with some embodiments of the present invention. Whilewater pressure in water body 50 such as a sea, ocean and/or lake varieswith depth of the water the air pressure in a tank 10 is typicallyconstant at any one time and is defined by a difference between theheight of water surface 78 of water body 50 and a height of watersurface 77 contained in tank 10. Typically, the pressure drop acrosswall 88 increases over height ‘H’ due to the varying pressure conditionsoutside tank 10. Typically, the greatest pressure drop occurs overhighest portion of the walls, e.g. near roof 48 and across roof 48 oftank 10. The present inventors have found that for utility sized tanks10, e.g. tanks, the tensile forces due to the pressure drops may besignificant and may potentially lead to bursting and/or cracking of tank10.

In the exemplary embodiment shown in FIG. 2, tank 10 has a height of 20meters (vertical height) and is anchored to a seabed 80 that is 501meters below sea level 78. When a water level 77 in tank 10 is low, tank10 is almost full with compressed air and the air pressure inside thestructure is determined from a difference in depth of water in tank 10,e.g. water level 77 and depth of water the seabed (or lakebed), e.g.water level 78. In this particular example, a water level 77 in tank 10is at a height of 1 meter above sea level 80, e.g. a depth of 500 metersfrom sea level 78 so that the air pressure in tank 10 is 51 ATM. The airpressure of 51 ATM is applied uniformly inside tank 10, e.g. on walls 88and ceiling 47 of tank 10 while the water pressure outside of tank 10changes over height H of tank 10 causing a pressure drop across walls 88and ceiling 47 (or roof 48) of tank 10. For example, at a depth of 490meters, water pressure outside of tank 10 is 50 ATM and the pressuredrop is 1 ATM. At a depth of 480 meters, water pressure outside tank 10is 49 ATM and the pressure drop is 2 ATM.

The present inventors have found that outward force 82 applied onceiling 47 (of roof) of tank 10 can be particularly large because force82 is a summation of upward pressure 82 applied to ceiling 47 due topressure drop and also due to buoyancy and/or flotation forces of tank10. According to some embodiments of the present invention, compartment40, e.g. an open compartment formed by roof 48 and banister 45 filledwith material 49, e.g. rocks, gravel and/or sand is adapted to apply agravitational force 84 to counterbalance upward force 82. Typically,weight of filling 40 is defined to match expected upward force 82. Thepresent inventors have found using weights to counter balance forcessimplifies construction of tank 10 and provides for adjustingcounterbalancing forces on site based on environmental conditions, e.g.depth that tank 10 is stored. In addition, weights such as sand androcks are easily attainable and typically inexpensive.

According to some embodiments of the present invention, compartment 40and/or banister 45 includes a door 60 that can be controllably opened torelease the weights 49 on demand. Optionally, the door 60 is opened andweights 49 are released from compartment 40 in cases when it is desiredto raise tank 10. In some exemplary embodiments, tank 10 is raised forrepair and/or for transporting tank 10 to an alternate site, e.g. havinga seabed at a different depth. Optionally, door 60 includes a latch orother mechanism that is controlled from above the water level 78. Insome exemplary embodiments, inlet/outlet duct 30 extends from ceiling 47of tank 10 and is surrounded by a shield 38 for protection againstpossible damage when pouring the weights over roof 48. Optionallyinlet/outlet duct is a flexible pipe.

Reference is now made to FIGS. 3A and 3B illustrating simplifiedschematic drawing of exemplary underwater energy storage systems withreinforced construction for withstanding pressure drops across walls ofthe storage tank in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention, wallsof tank 10 are reinforced to withstand pressure across walls 88 due toinherently higher pressure in the upper portion of tank 10 (with respectto the vertical direction) as compared to the water pressure outsidetank 10 at that level. According to some embodiments of the presentinvention, the reinforcements are designed to steadily increase withheight of walls 88 so that stronger reinforcement is provided in upperportions of walls 88 (with respect to vertical) where the pressure dropsacross walls 88 is larger.

Referring now to FIG. 3A, tank 10 is built with walls 88 having athickness that steadily increases with height so that the wall thicknessis thickest at a height where the pressure drop across the walls is thelargest and thinner where the pressure drop across the walls is smaller.Widening (or thickening) of the walls at upper portions of tank 10 mayalso provide additional support for ceiling 21. Optionally, tank 10additionally includes an external reinforcing belt 61 surrounding tank10 to reinforce the wall from the outside against blasting outwardly.

Referring now to FIG. 3B, in some exemplary embodiments, the walls oftank 10 are cast with reinforced concrete and the reinforcementsprovided are steadily increased with height of the walls, e.g. bysteadily increasing the diameter and/or the proximity of reinforcementbars added to the concrete or other casting material. In some exemplaryembodiments, reinforcement bars 62 used in lower portion of walls 88 aresmaller in diameter as compared to reinforcement bars 63 having largerdiameter. Optionally, reinforcement bars 62 in lower portion of tank 10are more sparsely distributed as compared to reinforcement bars, e.g.bars 62 or 64 in an upper portion of tank 10. Optionally, the proximitybetween bars is increased gradually over height of tank 10. In someexemplary embodiments, this gradual increase in wall strength providesfor withstanding gradually increasing forces due to increase pressuredrops across the wall along the height of the tank.

Optionally, tank 10 additionally includes internal walls 86 plated orcoated with a material other than the inner wall material, e.g.constructed from metal. In some exemplary embodiments, a thickness ofinternal walls is gradually increased (or in a step wise fashion) over aheight of tank 10 so that it provides increases reinforcement withheight to counterbalance the increased pressure drop across the wallsover the height of tank 10. Optionally, thickness 67 of internal wall 86in upper portion of internal wall 86 is larger than thickness 68 in alower portion of internal wall 86. Optionally, the thickness of theinternal walls increased by gradually increasing the number of layersmaking up the inner wall and/or maybe increased by increasing thethickness of the layer. Typically, internal wall 86 with varyingthickness provides a smooth internal surface.

It is noted that although it is possible to construct the wall withuniform strength, for utility sized underwater energy storage systems,the gradual reinforcements described herein may provide forsignificantly reducing the bill of materials.

Optionally, ceiling 47 is further reinforced by adding one or morepillars 69 extending from a floor 65 of tank 10 to ceiling 47.Optionally, further reinforcements may be in the form of a metalconstruction 64 extending between the walls 88 and at least partiallysupported by walls 88.

Reference is now made to FIGS. 4A, 4B and 4C illustrating simplifiedschematic drawings of exemplary underwater energy storage systemsincluding a storage tank whose diameter decreases as a function of tankheight in accordance with some embodiments of the present invention.According to some embodiments of the present invention, a tank 11 issubstantially cone shape and/or includes walls that taper over theheight ‘H’ of tank 11.

Referring now to FIG. 4A, optionally, weights 49 are poured over tank 11and are used to counter balance forces due to pressure drops andbuoyancy in the ceiling as well as on the walls. In some exemplaryembodiments, underwater energy storage system 100 includes a banister orwall 46 around walls of tank 11 providing a compartment in which weights49 are stored. Optionally, tank 11 is dome shaped. Optionally banister46 surrounds walls of tank 10 at a height above bottom of tank 11 andabove one or more water openings 20. According to some embodiments ofthe present invention, banister 49 includes one or more doors 60 thatcan be opened on demand to release weights 49. Optionally, doors 60 aremanipulated with a cable 51 from above the water. Optionally, theweights are added during or after submerging and are removed when it isdesired to float the tank to surface.

According to some embodiments of the present invention, the gravitationforce exerted on the walls by weights 49 at least partiallycounterbalances outward forces, e.g. tensile forces exerted on the wallsand ceiling of tank 11 due to a pressure drop across the walls 88 andceiling 47. According to some embodiments of the present invention, tank11 is shaped with a changing slope, e.g. dome shaped so that thecounterbalancing force provided by the weights has increasing forcecomponent in a direction perpendicular to walls for higher levels ofwalls 88 where the pressure drop is greater.

Referring now to FIG. 4B, in some exemplary embodiments, underwaterenergy storage system 100 includes a cone shaped (or bell shaped)underwater compressed gas storage tank 111 with concave shaped walls 89.In some exemplary embodiments, tank 111 is shaped so that a diameter ofcone shaped tank 111 at a given height multiplied by at a height abovethe floor 65 at that given height is a constant. For example for a tank111 that has a height ‘H’ of 10 meters, at a height of 1 meter abovefloor 65, the diameter of the tank may be 100 meters, at a height of 2meters above floor 65 the diameter of the tank may be 50 meters, at aheight of 5 meters the diameter of the tank will be 20 meters and at aheight of 10 meters the diameter of the tank may be 10 meters wide. Thepresent inventors have found that altering the diameter in this manner,a force, e.g. tensile force applied on walls 89 along the height ‘H’ oftank 111 due to pressure drop can be maintained constant although thepressure drop across the walls increases with height of tank 111.

Referring now to FIG. 4C, in some exemplary embodiments, the diameter ofan underwater compressed gas storage tank 112 is decreased in a stepwisefashion at defined heights of tank 112. In some exemplary embodiments,tank 112 is constructed from a plurality of stories that are fluidlyconnected through openings 23 between the stories. Typically, each storyabove a first story has a smaller diameter than the story under it. Insome exemplary embodiments, each story is cylindrical in shape and isassociated with a constant diameter. Optionally, one or more of thestories of tank 112 includes walls that taper over a height of thestory. Typically, compressed air is received from the uppermost storyvia air duct 30 and water openings 20 are provided on the lowest story.

Reference is now made to FIGS. 5A and 5B illustrating simplifiedschematic drawings of exemplary underwater energy storage systemsincluding a cylindrical storage tank that is partitioned in accordancewith some embodiments of the present invention. According to someembodiments of the present invention, underwater energy storage unit 100includes a cylindrical shaped tank 13 for storing compressed airincluding partitioning for reinforcing tank 13 against forces applied onit. According to some embodiments of the present invention, tank 13includes partitions that form chambers 71, e.g. sector shaped chambers.In some exemplary embodiments, inlet/outlet air duct 30 extends from oneor more of chambers 71. Optionally, air duct 30 is centered over tank 13and is open to each of chambers 71. In some embodiments of the presentinvention, chambers 71 include air openings 33 in upper portion of eachchamber that provides for air flow between inlet/outlet air duct 30 andeach of chambers 44. In some exemplary embodiments of the presentinvention, chambers 71 additionally include water openings 21 in abottom portion of each chamber 71 to allow free water flow betweenchambers 71. Typically, one or more of chambers 71 include wateropenings 20 providing water flow between tank 13 and water body 50.

Referring now to FIG. 5B, in some exemplary embodiments, underwaterenergy storage system 100 includes a compartment 41 for storing and/orreceiving weights 49 above a compressed air tank 13 that is constructedfrom walls 88 of tank 13 that are extended above ceiling of tank 13.According to some embodiments of the present invention, compartment 41includes partitioning walls that extend between walls 88 that dividecompartment 41 into sectors shaped compartments 73. In some exemplaryembodiments, partitioning walls 74 provide addition reinforcements towalls and ceiling for tank 13 against forces acting on tank 13.Optionally, partitioning walls 74, tank walls 88 and ceiling of tank 13are constructed as a single unit, e.g. formed from a single constructionfor added durability. In some exemplary embodiments, partitioning 74reinforces ceiling of tank 13 against breaking outwardly due to thepressure drop across ceiling.

According to some embodiments of the present invention, compartment 41includes one or more openings and/or doors 60 that can be opened ondemand to release weights 49. Optionally, a floor of compartment 41 isslanted down toward door 60 such that the weights fall out of thecompartment due to gravitational pull. Optionally, tank 13 includesreinforcing belt 61 around upper portion of tank 13 for additionalsupport of the walls 88.

Reference is now made to FIG. 6 illustrating a simplified schematicdrawing of exemplary underwater energy storage system including a cuboidstorage tank that is partitioned in accordance with some embodiments ofthe present invention. According to some embodiments of the presentinvention an underwater energy storage energy system 100, includes atank 12 that is cuboid shaped and includes partitioning walls 75 thatdivide the inner volume into smaller compartments 71, e.g. cuboid shapedcompartments. Typically partitioning walls 75 provide additional supportto a ceiling and walls of tank 12. According to some embodiments of thepresent invention, partitioning walls 75 include opening 33 for freeflow of air between compartments 71 and openings 21 for free flow ofwater between compartments 71.

Optionally, one or more air ducts 30 are connected through openings inone or only compartments 71 and air flow to and from duct 30 flowsthrough other compartments through openings 33. Typically, tank 12includes openings 20 for free water flow in and out of tank 12.Optionally, each compartment 71 has dedicated openings 20 providingwater flow communication between tank and water body 50 and there is nowater flow between compartments 71.

Reference is now made to FIGS. 7A and 7B illustrating simplifiedschematic drawings of exemplary underwater energy storage systemsincluding partitioned tank with reinforced walls around an air entrancechamber in accordance with some embodiments of the present invention.According to some embodiments of the present invention, compressed airstorage tank 10 is partitioned into a plurality of partitions 71, e.g.sector shaped partitions (FIG. 7A) or grid shaped partitions (FIG. 7B).Typically, each of the compartments includes air holes 33 through whichair can flow between compartments and to and from an inlet and/or outletair duct. According to some embodiments of the present invention, airflows in and out of tank 10 via one or more central chambers 37 throughwhich an inlet and/or outlet duct, e.g. duct 30, 31 and/or 32 connectsto tank 10. According to some embodiments of the present invention,walls 36 defining chamber 37 are constructed to be wider and/or havemore reinforcements than other walls of tank 10, e.g. walls 75.Optionally, walls 36 are constructed to withstand shockwaves that mayoccur as compressed air is feed into tank 10.

Reference is now made to FIG. 8 illustrating a simplified schematicdrawing of an exemplary underwater energy storage system including aplurality of inlet/outlet ducts that converge into a single duct inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, an air duct 331 branches intoa plurality of ducts 333. In some exemplary embodiments, each of ducts333 connect to one of a plurality of chambers 75. In some exemplaryembodiments, branching of air duct 331 provides reducing potentialpressure drop between different compartments 75. Optionally, reinforcingstructures 332 are added around a junction of the branching of ducts333.

Reference is now made to FIG. 9 illustrating a simplified schematicdrawing of an exemplary underwater energy storage system including aplurality of storage tank modules that are fluidly connected inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, underwater energy storagesystem 110 is constructed from a plurality of underwater compressed airstorage tanks 15 that are fluidly connected through air and/or gas ducts34 connected between tanks 15. According to some embodiments of thepresent invention, each of tanks 15 additionally includes one or morewater flow openings 20 allowing free flow of water into and out of eachtank 15. In some exemplary embodiments, each tank 15 includes acompartment 40 for receiving weights such as sand gravel and rocks asdescribed herein above.

According to some embodiments of the present invention, one or more airducts 30 is connected to one or a portion of the tanks 15 on a first endand to a compressor(s) and/or power generating unit(s) above sea level(or water level) at an opposite second end. According to someembodiments of the present invention, air flow through air duct 30extends or flows to all tanks 15 via air ducts 34. Alternatively, airduct 30 is replaced with air duct 331 (FIG. 8) that are partitioned intoa plurality of ducts, each of which is directly connected to one oftanks 15 so that air flow in and out of duct 30 is directly communicatedto each of tanks 15. Optionally in such a case, connecting air ducts 34are not required. The present inventors have found that constructing anunderwater energy storage system from a plurality of modular tanks 15that can be used together to provide energy to a single plant and/orenergy generating (or converting) unit, provides for adjusting a volumeof an underwater energy storage system without having to redesign and/orresize the underwater compression tank. Optionally, each tank 15 has auniform volume and shape. Alternatively, a number of different sizedtanks are manufactured that can be combined in different ways to meetthe demands of specific power sites. Constructing the underwater energystorage system with modular storage units, e.g. tanks 15 also providesfor reducing cost of the system since the size and shape of the tanksare standardized and do not have to be redesigned for different systems.

It is noted that although most of the embodiments of the presentinvention describe an underwater compressed air tank with a flat roof,other shaped roofs are also in the scope of the present invention.Optionally roofs of one or more of tanks 10, 12-16 may have othershapes, e.g. a convex or concave shape.

Reference is now made to FIGS. 10A and 10B illustrating simplifiedschematic drawings of exemplary underwater energy storage systemsincluding a floorless storage tank that is anchored at a height above aseabed in accordance with some embodiments of the present invention.According to some embodiments of the present invention, underwaterenergy storage system 200 includes a floorless or bottomless tank 230that is held at a defined height above a seabed 80 with one or moreanchors 231 and/or with an anchor 235 holding a net 234 encompassingtank 230. In some exemplary embodiments, tank 230 is a rigid tank.Typically, a rigid construction is more durable than known flexibleconstructions and maintains a constant volume. Typically, flexiblestructures are more susceptible to damage due biological and/or chemicalerosion occurring underwater or due to mechanical damage caused by fish,clams and the like that may damage flexibility of the bags and may tearor puncture the bags.

According to some embodiments of the present invention, tank 230 is heldat a height above a seabed. Optionally, the height over which tank 230is held enables unobstructed water flow 232 through open bottom 242 ofthe tank 230 even in cases when anchors 231 sink into the seabed.Typically, tank 230 includes an inlet/outlet air duct 30 connected tothe top of tank 230 through which compressed air is pumped in forstorage and/or released when energy to power a generator or device isrequired. Typically, tank 230 includes a volume of water 25 on a bottomportion of tank 230 and a volume of air 35 stored on an upper portion oftank 230. Typically, the level 77 of water in tank 230 is determined bythe amount of compressed air stored in tank 230. Optionally, tank 230 isdome shaped. Optionally, tank 230 is constructed from a flexible and/orcollapsible material. Optionally, tank 230 is in the form of a truncatedsphere (FIG. 10B), a cylinder, a cone, and/or a hemisphere. In someexemplary embodiments, tank 230 is held at a defined height above seabed80 with a net 234, e.g. a metal net that covers tank 230 and is held bya weight that may rest on seabed 80.

Reference is now made to FIG. 11 illustrates a simplified schematicdrawing of an exemplary underwater energy storage system partiallyformed from natural underwater landscape formations in accordance withsome embodiments of the present invention. According to some embodimentsof the present invention, underwater energy storage system includes atank 229 that is partially formed from existing under water structuressuch as walls of a canyon 220. In some exemplary embodiments, a roof 248and/or one or more walls are anchored onto the canyon 220 to form acompressed air tank 229 with an open bottom that allows free water flow232 from the bottom of the tank. Typically, compressed air is pumpedinto an upper portion of the tank with an air duct 30 and water entersthrough a bottom portion of tank 229. Optionally roof 248 is constructedfrom concrete casting.

Reference is now made to FIGS. 12A, 12B and 12C illustrating simplifiedschematic drawings of exemplary underwater energy storage systemsincluding a flexible storage bag in accordance with some embodiments ofthe present invention. According to some embodiments of the presentinvention, an underwater energy storage system 102 includes underwatercompressed air tank 230 that is partially formed with flexible and/orcollapsible material 241, e.g. a large plastic bag that forms an openbottom tank. In some exemplary embodiments, tank 230 is surrounded by aprotective cage 243, e.g. a metal grating to provide rigidity to tank230 and/or to strengthen construction of tank 230 (FIG. 12A).Optionally, a bottom 242 of tank 230 is maintained open by attachingcollapsible material 241 to a rigid rim and/or ring 251 of cage 243. Inother exemplary embodiments, tank 230 is not protected by a cage 243 buta rigid ring 251 is attached to open end of tank 230 (FIG. 12B) and isused to maintain tank 230 open and prevent it from collapsingcompletely. Typically, anchor 231 is attached to tank 230 through rigidstructure of ring 251 and/or of cage 243 to prevent tearing of material241. In yet other embodiments of the present invention, tank 230 isformed from a bag from flexible and/or collapsible material 241 that ismaintained at a height above a seabed 80 with a frame 244 that sits onseabed 80 (FIG. 12C). Optionally, frame 244 forms cavity and/or hollowspace 43 filled with rocks 49 providing a gravitation force foranchoring tank 230. In some exemplary embodiments, water flows freelyinto and out of tank 230 through water openings 20 and/or through duct22 formed in (or extending from) frame 244 to counterbalance inflow oroutflow of air 35 through inlet/outlet pipe 30.

Optionally, air tanks 230 may be particularly suitable when smallervolume tanks, e.g. having a diameter of a few meters, e.g. 5-10 metersare required. Typically, floorless air tanks, e.g. rigid or collapsibleare smaller and also cheaper to manufacture and may be suitable forsmaller scaled applications and/or as additions to larger scaledapplications. Optionally, air tanks 230, e.g. collapsible or rigid maybe particularly suitable for storing compressed air over a seabed thathas a sharp incline, over a seabed that is generally not flat, e.g. haslarge rocks and/or over a seabed that is generally not suitable forsupporting a large structure having a flat floor. In some exemplaryembodiments, tank 230 designed to float over a seabed provides a costeffective alternative to flattening out a rocky area of a seabed so thata tank may be positioned over the seabed.

Reference is now made to FIG. 13 illustrating a simplified schematicdrawing of an exemplary underwater energy storage system including aflexible compressed energy storage container housed in rigid storageunderwater tank in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention,underwater energy storage system 101 includes rigid storage tank 10 thatstores compressed soluble gases or fluids in a flexible bag 260 housedwithin rigid storage tank 10. Optionally, bag 260 stores condensedcarbonic gas. In some exemplary embodiments, the gases or fluids arefeed into bag 260 via duct 30 that extends above water level 78.Optionally the soluble gases and/or liquids are hazardous materials thatrequire storage in safe and stable conditions. Optionally, rigidconstruction of tank 10 protects container 260 from swaying and erosion,e.g. due to biological and/or chemical erosion or due to mechanicaldamage caused by fish, clams and the like that may damage flexibility ofthe bags. Typically, the rigid construction of tank 10 providesstability, anchoring and with holding pressures.

In some exemplary embodiments, tank 10 is anchored to a seabed andallows free water flow into and out of tank 10 through one or more waterchannels 20. Typically, free water flow through channels 20 provide forstabilizing pressure in tank 10. For example as more material is feedinto bag 260, bag 260 expands and water 25 is expelled from tank 10.Optionally, a flexible cable or line 231 is attached to a bottom of bag260 on one end and to floor 65 on another end to avoid jamming openingto air duct 30. Typically, inner walls 87 of tank 10 are smooth and/orrounded to protect bag 260 from being punctured. Optionally, inner walls87 are additionally coated with smooth low friction and/or frictionprotective materials such as various polymers.

Reference is now made to FIGS. 14A and 14B illustrating simplifiedschematic drawings showing an exemplary method for casting and sinkingan exemplary underwater storage system in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, an underwater energy storage system 1215 includesa metal or polymer frame or mold 170 that defines one or more tanks 171for storing energy, e.g. in the form of compressed air. In someexemplary embodiments, each tank 171 is fitted with a floor 65.Optionally, tank 171 does not include a floor. Optionally, the floor isa metal or polymer floor. Typically, frame 170 includes one or moreopenings though which water pipes 21 are fitted between neighboringtanks 171 and through which water ducts between the chambers and outsidewalls are fitted. Typically, frame 170 includes one or more openingsthrough which one or more inlet/outlet pipes 30 are fitted. In someexemplary embodiments, frame 170 additionally includes one or moreopenings through which air pipes 33 between neighboring tanks arefitted. According to some embodiments of the present invention, frame170 defines an inner portion and/or cavity 180 that can be filled withmaterial, e.g. concrete to complete construction of system 1215. In someexemplary embodiments, frame 170 is filled on site, e.g. aftertransportation to a desired sinking location.

According to some embodiments of the present invention, frame 170 istransported on water to a desired sinking location. Typically, duringtransport, water openings 20 are closed so that water does not entertanks 171. Optionally, once a desire sinking location is reached, system1215 is anchored with one or more anchors 213 so immobilize system 1215.Optionally, frame 170 is transported by a ship and a crane is used tolower frame into the water. According to some embodiments of the presentinvention, concrete is poured into cavity 180 while system 1215 isfloating over a desired sinking location. In some exemplary embodiments,a concrete mixer 176 brought to the spot on board a ship 177 or bargepours concrete into cavity 180 using a concrete pump 178 to fill cavity180. In some exemplary embodiments, air trapped in tanks 171 keepssystem 1215 afloat while the cement is being poured. Optionally one ormore buoys 196 are used keep system afloat while the cement is beingpoured.

According to some embodiments of the present invention, once the castingis completed and the casting is sufficiently dray, system 1215, valves23 on water openings 20 and valves 39 on air pipes 30 are opened and sothat water enters tanks 171 and system 1215 can sink to the desiredlocation. Optionally, if tanks 171 are floorless, channels 20 are alwaysopen and only valves 39 are opened to allow air release through pipe 30.In some exemplary embodiments, buoys, e.g. buoy chains are used tostabilize system 1215 and control the sinking speed.

Reference is now made to FIG. 15 illustrating an a simplified schematicdrawing of an exemplary underwater energy storage system including aninlet pipe for cooling compressed air in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, underwater energy storage system 104 includes aninlet pipe 31 through which compressed air flows from a compressor (notshown) to a compressed air tank 10. In some exemplary embodiments,compressed air pumped into pipe 31 is at a high temperature, e.g.hundreds of degrees Celsius and requires cooling prior to entering tank10. If air enters underwater tank 10 at significantly highertemperatures than surrounding environment, the temperature drop acrosstank 10 may cause cracks and/or damage to tank 10. In some exemplaryembodiments, inlet pipe 31 includes one or more heat exchange ribs alonga length of inlet pipe 31 to promote cooling of air flowing through pipe31. In some exemplary embodiments pipe 31 includes one or more ribs 55encompassing outer diameter 31 for enhancing heat exchange between water50 and air within pipe 31. Optionally, the outer ribs 55 shaped as flatrings. Optionally, outer ribs 55 are constructed to be aligned withwater currents typical found in an area where system 104 is situated.Optionally, rib 55 is a single spiral shaped rib that extends along alength of pipe 31. Optionally, walls of tank 10 include heat transferelements that are operable to release heat that may be stored in tank10. Optionally water outlet 22 provides a mechanism for releasing heataccumulated in tank 10.

Reference is now made to FIG. 16 illustrating a simplified schematicdrawing of an exemplary heat exchange and heat preservation system foruse with an underwater energy storage system in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, underwater energy storage system 105 is anadiabatic system (or semi-adiabatic system) that retains heat producedby compression and returns it to the air when the air is expanded togenerate power. Typically, during compression a large amount of heat iscreated in compressor 94 and inlet pipe 31 carrying air from compressorto underwater tank 10. In some exemplary embodiments, pipe 31 firstpasses through a fluid reservoir and/or a heat exchange pool 272 whereheat in pipe 31 is released. In some exemplary embodiments, reservoir272 is thermally isolated. Optionally, pipe 31 includes one or more ribs55 around a portion pipe 31 within fluid reservoir 272 for enhancingheat exchange within the reservoir. Optionally, compressor 94 includescooling ribs 95 that are additionally submerged in fluid of fluidreservoir 272 for cooling (submerging is not shown). Typically, heataccumulated rises in reservoir 272.

In some exemplary embodiments, heat accumulated in reservoir 272 risesto an upper portion of the tank and is used to heat air released fromtank 10 through pipe 32 prior to being used for operating a turbine 92.Typically, pipe 32 passes through an upper portion of reservoir 272where the heated fluid rises. Optionally, pipe 32 also includes one ormore ribs 55 around a portion of pipe 32 within reservoir 272 forenhancing heat exchange. Typically, heat exchange with pipe 32 resultsin cooling and cooled fluid flows to a bottom of reservoir 272 which canbe later used to cool air through pipe 31.

Reference is now made to FIG. 17 illustrating a simplified schematicdrawing of a variety of exemplary heat preservation pools for use withan underwater energy storage system in accordance with some embodimentsof the present invention. According to some embodiments of the presentinvention one or more air flow pipes 31 providing air flow from an aircompressor to an underwater compressed air storage tank 10 pass througha heat preservation pool 273 and/or a heat exchange unit to accumulateheat created during compression that can later be used for heating airdischarged from tank 10 (air discharge pipe is not shown). Typically airflow pipe includes ribs 55 for enhancing heat exchange. In someexemplary embodiments a pool 273 is constructed from an isolatingmaterial, e.g. a flexible or rigid isolating material and is filled withwater. Typically, a volume of pool 273 will depend on a volume of a tank10 and depth (or compression level) in which it is stored and willtypically be larger than thank 10. In one example, a tank 10 stored at adepth of about 400 meters may have a volume of about 30,000 m³ and anassociated pool 273 may have a volume of 10,000 m³. In some exemplaryembodiments, pool 273 floats in seawater 50. Optionally, buoys 281 areused to help pool 273 float. Optionally buoys 281 are also designed tocover water surface in pool and thereby prevent evaporation of the waterin pool 273. Alternatively and/or additionally, a pool 273 lies near abeach or on land and air flow pipes 31 pass through pools 273. In someexemplary embodiments, pool 276 is formed with a damn 278 constructed ata distance from a beach, and the seabed 80 between the damn and thebeach. Typically damn 278 extends above sea level 78 and separates abody of water from the sea to form pool 276. In some exemplaryembodiments, heat exchange is performed over surface water 78 and usedto condensed water vapors in air. Optionally, condensed water vapors 284are collected in a collection channel 285 and directed to a collectiontank 286. Optionally, condensed water vapors in collection tank 286 canbe used as a fresh water source.

Reference is now made to FIG. 18 illustrating an exemplary heat exchangeunit for desalinating water for use with an underwater energy storagesystem in accordance with some embodiments of the present invention.According to some embodiments of the present invention, an air releasepipe 32 gathers heat from the surroundings when the pressure begins tofall. Typically, air from pipe 32 cools significantly as pressure falls.In some exemplary embodiments, air from pipe 32 is conducted through alarger, thermally insulated pipe 312 around which a fluid with a lowfreezing temperature flows, e.g. through a vessel 313. In some exemplaryembodiments, discharged air is further heated by passing it through aheat reservoir 320 prior to using the air as an energy source, e.g. tooperate a turbine.

In some exemplary embodiments a pump 315 pumps fluid in vessel 313through a pipe system 314 and/or heat exchanging ribs 316. In someexemplary embodiments, heat exchanging ribs 316 are positioned over awater surface and due to cooling, water vapors 317 condense on them andflow down into a collection unit 319 including a collection tank 277.Alternatively, heat exchanging ribs 316 are immersed in sea water andthe cooling provided causes the surrounding water, e.g. water in acollection tank to freeze. Optionally, the thawed ice is collected andused as a fresh water source.

Reference is now made to FIGS. 19A and 19B illustrating simplifiedschematic drawings of exemplary thermal energy storage elements for usewith an underwater energy storage system in accordance with someembodiments of the present invention. According to some embodiments ifthe present invention, heat generated during air compression is storedin solid thermal storage elements. In some exemplary embodiments, thesolid thermal storage elements is formed from a solid ball 321, e.g. acement or ceramic ball for storing heat that includes one or more metalrods 322 that extend out of and/or through cement ball 322. Optionallymetal rods 322 is used enhance heat transfer into cement ball 322.Optionally, material other than metal is included in balls 321 toincrease heat transfer. Typically, rods 322 embedded in ball 322 enhanceheat exchange between the surrounding environment and cement balls 321.Optionally, a material in the form of a powder or small particles, e.g.nano-particles is used as solid thermal storage elements. The presentinventor has found adding material such as metal, e.g. such as rods 322,powder or small particles that has a high thermal conductivity tomaterials that can store heat, e.g. ceramics and concrete with lowthermal conductivity improves the efficiency thermal storage element.

According to some embodiments of the present invention, a pipe includinghigh temperature air flowing from a compressor to an underwatercompressed air tank passes through a reservoir filled with balls 321prior to entering into underwater storage tank. Heat dissipated from thepipe is stored in balls 321 for later use.

In some exemplary embodiments, a solid thermal storage element is in theform of a solid block 323, e.g. a cuboid or cylinder shaped block formedaround one or more inlet air pipes 31 and discharge air pipe 32.Typically, solid block is constructed from cement or a ceramic material.Optionally, the cement or ceramic is mixed with metal fibers or metalparticles for enhancing heat transfer. Optionally, ribs 324, e.g.running lengthwise along pipe 31 within solid block provide in enhancingheat exchange between air in pipes 31 and 32 and solid block 323.Optionally, heat accumulated in sold block 323 during off-peak hourswhen air is compressed and directed into an underwater storage tank, isstored in block 323 and later used to heat discharge air used togenerate power during peak hours.

It is noted that although most of the embodiments of the presentinvention have been described in reference to underwater energy storagesystems that are stored in the sea, the embodiments of the presentinvention are not necessarily limited in that respect and can also beapplied for underwater energy storing in other water bodies, e.g. lakesand reservoirs.

It is noted that although most of the embodiments of the presentinvention have been described in reference to storage of compressed air,other gases and/or fluids maybe stored with underwater energy storagesystem described hereinabove.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting. In addition, any priority document(s) of this applicationis/are hereby incorporated herein by reference in its/their entirety.

What is claimed is:
 1. An underwater energy storage system comprising: a tank for storing a compressed gas that is adapted to be stored underwater, wherein the tank encloses a constant volume, the tank comprising: at least one water opening through which water from surrounding environment can flow into and out of the tank; at least one gas opening through which the compressed gas is received; at least one duct communicating between the at least one opening for gas flow and a source of compressed gas; and a compartment constructed over a roof of the tank, wherein said compartment is adapted for receiving weights at a sinking site of the tank.
 2. The system of claim 1, wherein the compartment is formed with a banister encompassing the roof of the tank.
 3. The system of claim 2, wherein the banister is an integral part of walls of the tank that extends above a height of the roof.
 4. The system of claim 1, wherein the compartment is partitioned with partitioning walls adapted to provide structural support for the roof of the tank.
 5. The system of claim 2, wherein the tank includes sloped walls, and wherein the banister at least partially encompasses the walls of the tank.
 6. The system of claim 1, wherein the compartment includes a door, wherein the door provides for releasing weights received in the compartment when opened.
 7. The system of claim 1, wherein the weights include at least one of rocks, sand and gravel.
 8. The system of claim 1, wherein the tank includes walls that have a thickness that increases over a height of the walls.
 9. The system of claim 1, wherein the tank includes walls with structural reinforcements, wherein an amount of the reinforcement provided increases over a height of the tank.
 10. The system of claim 1, wherein the tank is partitioned into a plurality of chambers, said chambers include chamber walls with gas openings that provide free gas flow between the chambers and wherein each of the chambers includes water opening through which water from surrounding environment can flow.
 11. The system of claim 10, wherein a chamber wall that surrounds a chamber that directly communicates with the at least on duct through which the compressed gas is received, is provided with added reinforcements.
 12. The system of claim 10, wherein the at least one duct through which the compressed gas is received branches into a plurality of ducts each of which directly communicates with one of the chambers of the tank.
 13. The system of claim 1, comprising: a plurality of tanks; and gas ducts connected between gas openings of each of the plurality of tanks, wherein the gas ducts provide free gas flow between the plurality of tanks.
 14. The system of claim 1 comprising a water duct connected the at least one water opening and extending upward therefrom, said duct adapted to provide a water opening at a height above the water opening of the tank.
 15. The system of claim 1, comprising an extension extending from a floor of the tank, the extension defining an open channel in which weights can be contained for anchoring the tank on a bed of a water body.
 16. The systems of claim 1, wherein the tanks includes prongs extending outward from a floor of the tank, wherein said prongs are adapted to be embedded in a bed of a water body for stabilizing the tank on the bed of the water body.
 17. The system of claim 1, wherein the tank is casted with concrete.
 18. The system of claim 1, wherein the tank includes inner walls that are coated with a metal layer.
 19. The system of claim 18, wherein a thickness of the metal layer increases over a height of the tank.
 20. The system of claim 1, wherein the tank includes outer walls that are coated with a metal layer.
 21. The system of claim 1, wherein the at least one duct communicating between the at least one opening for gas flow and a source of compressed gas is lined with a plurality of ribs adapted to cool the compressed gas as it flows from the source to the tank.
 22. The system of claim 21, wherein at least a portion of the ribs are outer ribs that encompass an outer diameter of the duct and wherein the outer ribs are structured to be in line with a direction of current flow in the sinking site of the system.
 23. The system of claim 1, comprising at least one duct communicating between the at least one opening for gas flow in the tank and a pneumatic device.
 24. The system of claim 23, comprising a heat exchange unit for transferring heat generated by the source of compressed gas to gas flowing from the at least one duct communicating between the at least one opening for gas flow in the tank and a pneumatic device.
 25. The system of claim 24, wherein the heat exchange unit includes a heat exchange pool formed between a damn constructed at a distance from a beach and the beach.
 26. The system of claim 24, wherein the heat exchange unit includes at least one thermal energy storage element through which the at least one duct communicating between the at least one opening for gas flow and a source of compressed gas and the at least one duct communicating between the at least one opening for gas flow in the tank and a pneumatic device pass through.
 27. The system of claim 23, comprising a heat exchange unit adapted to harness cooling of gas discharged from the tank for desalinating water.
 28. The system of claim 1, wherein the compressed gas is air.
 29. The system of claim 1, wherein the compressed gas is carbonic gas.
 30. The system of claim 1, wherein the tank includes a floor. 